Author: Sam Mottram, Keith Ainsley, Egbert Scherman
Conference: 84th Annual Meeting of International Commission on Large Dams
Date: May 15-20, 2016

ABSTRACT
The exclusion of sediment for hydropower intakes and the flushing of sediment from reservoirs in order to maintain live storage are critical to the long- term viability and sustainability of hydroelectric projects around the World. This paper presents several design innovations and case studies of run-of-river diversion dams and intakes incorporating inflatable rubber dams, vortex de-sanders and Coanda screen intakes for sediment exclusion and flood passage. It presents the findings of physical and CFD model tests, case studies of operating facilities and lessons learned. The projects showcased include:

• The 147 MW East Toba Hydroelectric Project with inflatable rubber dam for sediment scouring and flood passage.
• The largest capacity Coanda Screen intake in the World on the 45 MW Kokish River Hydroelectric Project, designed for sediment exclusion and fish passage.
• Case studies and lessons learned from 8 other run- of- river hydroelectric projects recently constructed that use crest gates (i.e. rubber dams, Obermeyer crest gates or similar) and/or Coanda Screen intakes for sediment flushing and exclusion.

INTRODUCTION
Run-of-river hydroelectric projects typically do not have large storage reservoirs upstream of their intakes, reservoirs that would have sufficient volume and depth to accommodate the exclusion of sediment through settling. Figure 1 below shows the schematic layouts of a typical large hydro storage dam versus a run- of- river hydroelectric facility. A typical run-of-river intake is designed to efficiently divert the hydroelectric project’s generation flow into the water conveyance system and as much as practical eliminate sediment from entering the power facilities. Sediment exclusion for run-of-river intakes has historically been managed using desanding basins, large complex structures that are costly to operate and add significantly to the overall project capital cost.

This paper will illustrate various alternatives to using large desanding basins. These alternatives have proven to be effective at sediment flushing and exclusion, while also being very cost effective and thereby increasing the likelihood of the run-of-river projects being economically viable. Technologies that Knight Piésold have implemented in the design of run-of-river intakes include:

• Reservoir De-sander Type Intake – using the upstream head pond as the primary sediment settling basin
• Coanda Screen Type Intake – where a fine screen is used to physically separate sand particles from the diversion flow using the Coanda shear effect
• Combination of Coanda Screens and Reservoir De-sanding

Several case studies are provided illustrating the application of each technology and the findings of
physical and computer based model testing completed to support each design, as well as the lessons learned from commissioning and operating the facilities.

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